This disclosure relates to a moderated nuclear fuel composition for providing a desired prompt negative reactivity coefficient.
Nuclear fuels used in fast reactors as breeders, actinide burners, or power reactors typically exhibit relatively small or negligible negative prompt coefficients of reactivity. One reason for this is a lack of Doppler broadening in such fuels. For instance, neutron energies in a typical nuclear fuel of a fast reactor are much greater than nuclei resonance ranges where Doppler broadening occurs. Neutron energies may be several hundred keV and Doppler broadening may occur primarily below 25 keV. As a result, the prompt coefficient of reactivity of the nuclear fuel is weak or negligible. Additionally, voiding in the surrounding coolant removes parasitic neutron absorption and causes a positive coolant void coefficient, which is generally an undesirable condition.